Clinical Biomechanics - Articles in Press

Patellar tendon repair with hamstring autograft: A cadaveric analysis - Corrected Proof

William M. Mihalko, Matthew Vance, Marc J. Fineberg — 2010-02-04

Abstract: Background: Rupture of the patellar tendon requires surgical repair to restore function of the knee. The most accepted repair technique utilizes running locking non-absorbable sutures secured to the patella through three drill holes. Complications with this repair technique include rerupture, knee stiffness, and extensor lag caused by gap formation at the site of repair. Some surgeons have suggested augmenting the standard repair with local autograft tendon to avoid these complications. It was hypothesized that using a repair technique that included augmentation of the repair with autograft tendons would decrease the gap formation at the repair site under cyclic loading conditions.Methods: In this experiment, eight specimens were used to analyze two methods of patellar tendon repair: hamstrings autograft augmentation and a standard repair using three vertical bone tunnels in the patella. Each specimen was then extended with a 2.2kg weight on the tibia at 0.25Hz to simulate early motion after surgery. The gap formed at the repair site was then measured at 1, 10, 100, and 250cycles and both techniques confidence interval compared using a Wilcoxon signed rank test.Findings: The mean gap formation for the standard repair after one cycle was 8.9mm (SD 2.4) and for the augmented repair was 3.6mm (SD 0.9). At 250cycles the mean gap formed for the standard repair was 13.2mm (SD 1.9) and the mean gap for the augmented repair was 7.2mm (SD 0.9). All gaps for all cycles analyzed had an 88% confidence interval for significance using a Wilcoxon signed rank test.Interpretation: The biomechanical results of this study show statistical trend toward decrease gap formation with an augmented tendon at the repair site under a simulated dynamic knee motion.

Primary stability of custom and anatomical uncemented femoral stems: A method for three-dimensional in vitro measurement of implant stability - Corrected Proof

Per Olav Østbyhaug, Jomar Klaksvik, Pål Romundstad, Arild Aamodt — 2010-02-03

Abstract: Background: Lack of primary stability of cementless hip stems prevents bone ingrowth and may lead to loosening of the stem. Direct measures of the implant stability require drilled holes in the bone at the measuring site. These holes weaken the cortical bone, limit the number of possible measuring points and inhibit other biomechanical measurements. This in vitro study aimed to develop a method for indirect measurement of primary stability of femoral stems, leaving the specimen intact. The method was used to compare the primary stability of two uncemented femoral stems with different proximal fit and fill and different stem length.Methods: An in vitro method for indirect full three-dimensional measurement of implant–bone interface motion was developed. Uncemented customized (n=10) and anatomical stems (n=10) were inserted in human cadaver femora and the primary stability during one leg stance and stair climbing was measured.Findings: The method had high precision, and the errors due to necessary assumption of rigid body components were minimal. The customized stem with optimal proximal fit and fill provided the best initial stability for rotation in retroversion. The anatomical stem with longer stem length was more resistant to permanent rotation in varus.Interpretation: During stem design development the primary stability can be measured at all wanted measuring sites with the presented method, leaving the specimen intact for further analyses.

Nonlinear and anisotropic tensile properties of graft materials used in soft tissue applications - Corrected Proof

Jonathon H. Yoder, Dawn M. Elliott — 2010-02-03

Abstract: Background: The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson’s ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT.Methods: The degree of anisotropy and non-linearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue.Findings: The Alloderm graft was anisotropic in both the toe- and linear-region of the stress–strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress–strain responses, were largely isotropic, had a linear-region modulus of 18MPa, and were nonlinear. OrthADAPT was anisotropic in the linear-region (131 MPA vs 47MPa in the toe-region) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0.Interpretation: Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application.

Three-dimensional stereoradiographic modeling of rib cage before and after spinal growing rod procedures in early-onset scoliosis - Corrected Proof

2010-02-03

Abstract: Background: Early-onset scoliosis frequently leads to major thoracic deformity and pulmonary restrictive disease. Growing rods surgical techniques were developed to achieve a satisfactory correction of the spinal curves during growth. The effect on the rib cage deformity has not yet been documented. The purpose of this study was to analyze the changes of the thoracic geometry after implantation of a growing rod, and to evaluate a stereoradiographic reconstruction method among young scoliotic patients.Methods: Four patients were enrolled in the study, and four additional patients in the reproducibility study. Three-dimensional spine and rib cage models were generated after low-dose stereoradiographic imaging (EOS). Three-dimensional parameters were computed before and after surgery. Intra and inter-observer reproducibility was calculated, and the accuracy was assessed in comparison to volumetric CT-scan.Findings: The average Cobb angle was reduced from 50.8° to 26°. The surgery resulted in a complex 3D effect on the rib cage, combining frontal, lateral, and axial rotation. This effect was dependent of the side (concave or convex), and the position relative to the apical vertebra. Mean errors in comparison to CT-scan were 3.5mm.Interpretation: The results on the spinal deformity are comparable to other series. The effect on the rib cage is of a smaller magnitude than in the case of a spinal arthrodesis. A longer follow-up is necessary to confirm the positive effect on the rib cage deformity. Further research should be performed to improve the reproducibility of 3D parameters.

Biomechanical study of posterior wall acetabular fracture fixation using acetabular tridimensional memory alloy-fixation system - Corrected Proof

Liu Xin-wei, Xu Shuo-gui, Zhang Chun-cai, Fu Qing-ge, Wang Pan-feng — 2010-02-03

Abstract: Background: We developed the acetabular tridimensional memory alloy-fixation system (ATMFS), which is made of NiTi shape memory alloy, according to the specific mechanical properties of biological memory material, nitinol alloy and measured distribution of contact area and pressure between the acetabulum and the femoral head of cadaveric pelvis.Methods: Six formalin-preserved cadaveric pelvis were used for this investigation. Pressure-sensitive film was used to measure contact area and pressure within the anterior, superior, and posterior regions of the acetabulum. The pelvis were loaded under the following four conditions: (1) intact; (2) following a creation posterior wall fracture defect; (3) following reduction and standard internal fixation with reconstruction plate; (4) following reduction and internal fixation with a new shape memory alloy device named ATMFS. A posterior wall fracture was created along an arc of 40–90° about the acetabular rim.Findings: Creation of a posterior wall defect resulted in increased load in the superior acetabulum (1422N) as compared to the intact condition (762N, P=0.007). Following reduction and internal fixation, the load distributed to the superior acetabulum (1486N) was not statistically different from the defect condition. Following the fixation with ATMFS, the load seen at the superior region of the actabulum (936N) was less than fixation with reconstruction plate and was not different from intact state (P=0.4).Interpretation: These data indicate that the use of ATMFS as a fracture internal fixation device resulted a partial restoration of joint loading parameters toward the intact state. ATMFS fixation may result in a clinical benefit.

Biomechanical effects of patellar positioning on intraoperative knee joint gap measurement in total knee arthroplasty - Corrected Proof

2010-02-01

Abstract: Background: Balancing both the lateral/medial and extension/flexion joint gaps is a prerequisite for soft tissue balance in total knee arthroplasty. The purpose of this study was to quantify the effects of patellar positioning and quadriceps load during total knee arthroplasty on knee joint gap measurements.Methods: Eight fresh-frozen cadaveric knees ranging in age from 65 to 85years old were used. Using a medial parapatellar approach, posterior cruciate ligament sacrificing total knee arthroplasty was performed. The specimens were mounted on a custom knee testing system that allowed the femur to be locked in position for knee extension or flexion. Patellar positions of eversion, reduction, and following repair of the arthrotomy were examined. The influence of quadriceps muscle load was investigated by varying the quadriceps load from 0 to 125N. The lateral and medial joint gaps, represented by the distance from the implanted femoral component surface to the cut tibia surface, were measured with 100N tibial distraction force using a 3D digitizer in both extension (0°) and flexion (90°).Findings: Both the medial and lateral joint gaps with patella eversion were significantly smaller than those with patellar reduction and arthrotomy repair (extension: all quadriceps loads, P<0.0002; flexion: quadriceps loads less than 75N, P<0.0002). In patella eversion, quadriceps loading decreased the lateral joint gap more than the medial joint gap in both extension and flexion; however, the effect was greater in knee flexion with significant differences seen at all quadriceps loads, whereas in extension significant differences were only seen for quadriceps loading of 75N and greater. Patella eversion also caused a lateral-posterior shift and external rotation of the tibia compared to the other conditions (P<0.005). With patella reduction and repair of the arthrotomy lower quadriceps loading decreased the extension gap significantly more than the flexion gap (P<0.01). Following repair of the arthrotomy higher quadriceps loading significantly decreased the flexion gap more than the extension gap (P<0.04).Interpretation: The patellar positioning and quadriceps muscle loading in total knee arthroplasty have a strong influence on intraoperative joint gap measurements.

Vibration measurements predict the mechanical properties of human tibia - Corrected Proof

Bekir Bediz, H. Nevzat Özgüven, Feza Korkusuz — 2010-01-28

Abstract: Background: Vibration analysis is a promising technique in diagnosing metabolic bone diseases such as osteoporosis and monitoring fracture healing. The aim of this study is to observe the structural dynamic property changes of the tibia extracted from the vibration analysis data.Methods: In this study, bone mineral density and vibration measurements were made both in in vivo and in vitro conditions. The relationship between structural dynamic properties, obtained and bone mineral densities measured were investigated. Also, the effect of soft tissues on measured structural dynamic properties was analyzed.Findings: Natural frequency of the tibia decreased with decreasing bone mineral density that presented a weak correlation with the bone mineral density values measured by dual energy X-ray densitometer of the femur. In the case of in vitro experiments, it was observed that the effect of muscles on measurement results is higher than that of the effect of the skin and the fibula which makes the modal identification procedure difficult. However, having very large percentage changes in the loss factors when mineral content and collagen are reduced is an encouraging result to believe that damping measurements may yield a promising technique in diagnosing progressing osteoporosis and monitoring fracture healing period.Interpretation: The utilization of natural frequency alone as a diagnosing tool does not seem to be a sufficient method although there is a correlation between this parameter and bone mineral density. However, in vitro experiments showed that the identification of the loss factor is a promising technique in diagnosing progressing osteoporosis.

Upper limb joint dynamics during manual wheelchair propulsion - Corrected Proof

2010-01-27

Abstract: Background: Inverse dynamic methods have been widely used to estimate joint loads during manual wheelchair propulsion. However, the interpretation of 3D net joint moments and powers is not always straightforward. It has been suggested to use joint coordinate systems (expression of joint moment on anatomical axes) and the 3D angle between joint moment and angular velocity vectors (propulsion, resistance or stabilization joint configuration) for a better understanding of joint dynamics.Methods: Nine spinal cord injured subjects equipped with reflective markers propelled in a wheelchair with an instrumented wheel. Inverse dynamic results were interpreted using joint coordinate systems, 3D joint power and the 3D angle between the joint moment and joint angular velocity vectors at the three upper limb joints. The 3D angle was used to determine if the joints were predominantly driven (angle close to 0 or 180 degrees) or stabilized (angle close to 90°).Findings: The wrist and elbow joints are mainly in a stabilization configuration (angle close to 90°) with a combination of extension and ulnar deviation moments and an adduction moment respectively. The shoulder is in a propulsion configuration, but close to stabilization (angle hardly below 60°) with a combination of flexion and internal rotation moments.Interpretation: Stabilization configuration at the joints could partly explain the low mechanical efficiency of manual wheelchair propulsion and could give insight about injury risk at the wrist, elbow and shoulder joints.

Sagittal plane knee joint moments following anterior cruciate ligament injury and reconstruction: A systematic review - Corrected Proof

Joseph M. Hart, Jia-Wei Kevin Ko, Tim Konold, Brian Pietrosimione — 2010-01-25

Abstract: Background: Gait adaptations in persons with anterior cruciate ligament (ACL) injuries have been debated. Many studies examine high speed, 3-dimensional video gait analysis to compare knee joint torques during simulated activities of daily living.Methods: We performed a systematic review of the literature for published clinical papers that reported sagittal plane knee joint kinetics in ACL deficient or reconstructed individuals. We calculated weighted effect sizes (Cohen’s d) to evaluate the magnitude of differences between the injured limb and the contralateral limb and healthy, uninjured limbs in control subjects.Findings: Ten published papers reported kinetic data in ACL deficient subjects while walking for comparisons to the contralateral side (weighted average d=−0.83, range: −3.21, 1.07), and to healthy control knees (weighted average d=−1.0, range: −3.36, 0.17); four papers reported data during jogging compared to the contralateral side (weighted average d=−0.94, range: −4.15, 0.17), and to controls (weighted average d=−1.42, range: −3.83,−0.2). Four papers reported data for ACL-reconstructed patients compared to healthy controls during walking (weighted average d=−0.94, range: −0.4, −1.77) and jogging (weighted average d=−1.18).Interpretation: Effect sizes comparing knee joint moments in injured vs. healthy control subjects appear to be slightly higher while jogging than walking, and higher in ACL-deficient patients compared to reconstructions. However, magnitudes are all large. Few studies report stair climbing. Consequently, it is difficult to make inferences with confidence during these tasks.

Effects of running speed on a probabilistic stress fracture model - Corrected Proof

2010-01-25

Abstract: Background: Stress fractures are dependent on both loading magnitude and loading exposure. Decreasing speed is a potential mechanism of strain reduction during running. However, if running speed is decreased the number of loading cycles will increase for a given mileage. It is unclear if these increased loading cycles are detrimental despite reductions in bone strain. The purpose of this study was to determine the effects of running speed on the probability of tibial stress fracture during a new running regimen.Methods: Ten male subjects ran overground at 2.5, 3.5, and 4.5m/s. Force platform and kinematic data were collected synchronously. Inverse dynamics and musculoskeletal modeling were used to determine joint contact forces acting on the distal tibia. Peak tibial contact force served as input to a finite element model to estimate tibial strains. Stress fracture probability for each running speed was determined using a probabilistic model based on published relationships of bone damage, repair, and adaptation. The effects of speed on stress fracture probability was compared using a repeated measures ANOVA.Findings: Decreasing running speed from 4.5 to 3.5m/s reduced the estimated likelihood for stress fracture by 7% (P=0.017). Decreasing running speed from 3.5 to 2.5m/s further reduced the likelihood for stress fracture by 10% (P<0.001).Interpretation: Runners wanting to reduce their risk for tibial stress fracture may benefit from a decrease in running speed. For the speeds and mileage relative to the current study, stress fracture development was more dependent on loading magnitude rather than loading exposure.

How do visual, spectroscopic and biomechanical changes of cartilage correlate in osteoarthritic knee joints? - Corrected Proof

2010-01-22

Abstract: Background: Characteristic changes in cartilage of human knee joints with different degrees of osteoarthritis (OA) have been investigated by visual, biophotonical and biomechanical examination. Knowledge about the cartilage composition and changes during the development of OA is important for diagnostic decisions and understanding the pathogenesis of OA.Methods: Thirty two patients with severe knee OA received endoprosthetic replacement. During surgical intervention cartilage specimen were harvested from defined surface areas of the joints. The degree of cartilage defects was classified visually (ICRS Grade: International Cartilage Repair Society), biophotonically (NIRS: near infrared spectroscopy) and biomechanically (Young’s Modulus). To characterise links between the investigated parameters the Spearman’s rank correlation coefficient was used.Findings: Significant negative correlations were found between visual macroscopic degree of degeneration (ICRS Grade) and biophotonic characteristics (NIRS) (ρ=−0.467) or cartilage stiffness (Young’s Modulus) (ρ=−0.501). Between NIRS and Young’s Modulus significant positive correlation of ρ=0.535 was detected.Interpretation: Visual, biophotonic and biomechanical properties of cartilage reveal strong correlations in all degrees of cartilage defects in patients with severe OA. According to these results, we indicate that an objective, non-invasive and non-destructive measurement of cartilage properties during open and arthroscopic knee surgery is possible by NIRS and provide a novel tool to evaluate disease intervention and treatment.

Fixed-angle plate osteosynthesis of the patella – An alternative to tension wiring? - Corrected Proof

M. Wild, C. Eichler, S. Thelen, P. Jungbluth, J. Windolf, M. Hakimi — 2010-01-22

Abstract: Background: The goal of this study is carry out a biomechanical evaluation of the stability of a bilateral, polyaxial, fixed-angle 2.7mm plate system specifically designed for use on the patella. The results of this approach are then compared to the two currently most commonly used surgical techniques for patella fractures: modified anterior tension wiring with K-wires and cannulated lag screws with anterior tension wiring.Methods: A transient biomechanical analysis determining material failure points of all osteosyntheses were conducted on 21 identical left polyurethane foam patellae, which were osteotomized horizontally. Evaluated were load (N), displacement (mm) and run-time (s) as well as elastic modulus (MPa), tensile strength (MPa) and strain at failure (%).Findings: With a maximum load capacity of 2396 (SD 492) N, the fixed-angle plate proved to be significantly stronger than the cannulated lag screws with anterior tension wiring (1015 (SD 246) N) and the modified anterior tension wiring (625 (SD 84.9) N). The fixed-angle plate displayed significantly greater stiffness and lower fracture gap dehiscence than the other osteosyntheses. Additionally, osteosynthesis deformation was found to be lower for the fixed-angle plate.Interpretation: A bilateral fixed-angle plate was the most rigid and stable osteosynthesis for horizontal patella fractures with the least amount of fracture gap dehiscence. Further biomechanical trials performed under cycling loading with fresh cadaver specimen should be done to figure out if a fixed-angle plate may be an alternative in the surgical treatment of patella fractures.

A comparison of the quasi-static mechanical and non-linear viscoelastic properties of the human semitendinosus and gracilis tendons - Corrected Proof

Steven D. Abramowitch, Xiaoyan Zhang, Molly Curran, Robert Kilger — 2010-01-21

Abstract: Background: Over 50-% of anterior cruciate ligament reconstructions are performed using semitendinosus and gracilis tendon autografts. Despite their increased use, there remains little quantitative data on their mechanical behavior. Therefore, the objective of this study was to investigate the quasi-static mechanical and non-linear viscoelastic properties of human semitendinosus and gracilis tendons, as well as the variation of these properties along their length.Methods: Specimens were subjected to a series of uniaxial tensile tests: 1-h static stress-relaxation test, 30 cycle cyclic stress-relaxation test and load to failure test. To describe the non-linear viscoelastic behavior, the quasi-linear viscoelastic theory was utilized to model data from the static stress-relaxation experiment.Findings: The constants describing the viscoelastic behavior were similar between the proximal and distal halves of the gracilis tendon. The proximal half of the semitendinosus tendon, however, had a greater viscous response than its distal half, which was also significantly higher than the proximal gracilis tendon. In terms of the quasi-static mechanical properties, the properties were similar between the proximal and distal halves of the semitendinosus tendon. However, the distal gracilis tendon showed a significantly higher tangent modulus and ultimate stress compared to its proximal half, which was also significantly higher than the distal semitendinosus tendon.Interpretation: The results of this study demonstrate differences between the semitendinosus and gracilis tendons in terms of their quasi-static mechanical and non-linear viscoelastic properties. These results are important for establishing surgical preconditioning protocols and graft selection.

The association between external-ground-reaction force and knee-joint kinetics during partial- and full-weight-bearing gait - Corrected Proof

Jay R. Ebert, David G. Lloyd, Anne Smith, Timothy Ackland, David J. Wood — 2010-01-21

Abstract: Background: Progressive weight-bearing is recommended following autologous chondrocyte implantation. This weight-bearing program assumes that increasing external loads experienced at the foot during gait are closely related to external-knee-joint moments. We investigated this relationship, and examined other variables that may contribute to knee-joint kinetics of which the clinician can modify using practical instruction within a clinical setting.Methods: Gait analysis was performed in 51 patients following autologous chondrocyte implantation, during various partial- and full-weight-bearing conditions. The contribution of ground-reaction force, kinematic and spatio-temporal gait parameters to external-knee moments was investigated within weight-bearing levels less than 60%, between 60% and 90% and more than 90% of individual body weight.Findings: There was no association between peak-ground-reaction force and the knee-adduction moment within the 60–90% and more than 90% weight-bearing conditions, nor the peak-knee-flexion moment at less than 60% weight-bearing. Peak-ground-reaction force accounted for no more than 21.4% and 18.6% of the variance in the knee-adduction and flexion moments, respectively, within any weight-bearing condition, while the combination of peak-ground-reaction force, kinematic and spatio-temporal parameters investigated accounted for no more than 39.7% and 52.2%, respectively. Foot-progression angle and knee-flexion during weight acceptance accounted for a significant (P<0.05) portion of the variance in external-knee moments, particularly at higher levels of weight-bearing.Interpretation: A large amount of variance in knee moments may be attributed to variables other than external loads, some of which can be modified by the clinician. Clinically, this is important for any therapist implementing progressive weight-bearing protocols.

Patients with osteoarthritic knees have shorter orientation and tangent indicatrices during gait - Corrected Proof

Michael Raymond Pierrynowski, Patrick A. Costigan, Monica R. Maly, Peter T. Kim — 2010-01-20

Abstract: Background: This study introduces two novel outcomes that could be used to identify people with knee osteoarthritis from healthy controls. These outcomes examine the lengths of paths on a sphere derived from knee angle and knee position during gait.Methods: Participants with moderate knee osteoarthritis (n=47) and no knee pathology (n=51) walked overground. The time-varying orientation matrices and position vectors of the knee (leg relative to the thigh) were measured, then arclength (constant speed) parameterized. The orientation matrix column aligned with the long axis of the leg, and the tangent, normal and binormal vectors (Frenet Frame) along the position vectors were calculated. These unit length vectors all scribe paths (indicatrices) on a unit sphere. The path lengths of these indicatrices, for all or part of a gait cycle, were the novel outcomes. A stepwise discriminant analysis defined a linear function that included those outcomes that best allocated a participant to the osteoarthritis or control group.Findings: Group differences were best detected with the indicatrix lengths associated with the orientation of the leg’s long axis over a gait cycle (P<0.001) and the tangent vector over the stance phase (P=0.014). Both outcomes were smaller in the knee osteoarthritis compared to control group. Walking speed was poorly correlated with all indicatrix lengths (ρ<|0.484|) and a discriminate analysis correctly classified 83.7% of the participants.Interpretation: Smaller indicatrix measures distinguished those with knee osteoarthritis from healthy controls. These outcomes introduce a promising new kinematic approach when examining gait data.

Mechanical properties of glenoid cancellous bone - Corrected Proof

2010-01-18

Abstract: Background: Loosening of the glenoid component in total shoulder arthroplasty is the main late complication of this procedure; it may be assumed that it is highly dependent on the quality of the glenoid cancellous bone. Very little is known about the mechanical properties of this cancellous bone. The aim of this study was to determine these properties (Young’s modulus and strength) as well as bone density in different parts of the glenoid cancellous bone to assess their variations.Methods: Eleven scapulas were obtained from six fresh-frozen, unembalmed human cadavers. Eighty-two cubic cancellous bone specimens were extracted and tested using a uniaxial compression test; then the specimens were defatted and correlations with bone density were determined.Findings: The study showed significant differences in the mechanical properties with anatomic location and directions of loading. Young’s modulus and strength were found to be significantly higher at the posterior part of the glenoid with the weakest properties at the antero-inferior part. Cancellous bone was found to be anisotropic with higher mechanical properties in the latero-medial direction perpendicular to the articular surface of the glenoid. The apparent density was on average equal to 0.29g/cm3 with the higher values at the posterior and superior part of the glenoid. Good correlation between apparent density and elastic modulus was found only in the sagittal planes but not in the coronal and axial plane.Interpretation: The mechanical properties determined in this study showed the anisotropy of the glenoid cancellous bone; values of these properties could provide input data for finite element method analyses in shoulder prosthesis designs.

Stability and variability of knee kinematics during gait in knee osteoarthritis before and after replacement surgery - Corrected Proof

2010-01-11

Abstract: Background: Patients with knee osteoarthritis often feel unstable, suffering from buckling (giving way) or even falling. This study aimed at characterising such instability, and following it over time.Methods: We investigated treadmill walking in knee osteoarthritis, focusing on angular velocity of sagittal plane knee movements. Knee osteoarthritis patients were followed 1year after replacement surgery, and were compared to healthy peers. Subjects walked at increasing speeds, and maximum speed was registered. To quantify stability, we calculated short-term (λS) and long-term (λL) Lyapunov exponents (the exponential rate of divergence, in state space, of trajectories originating from nearest neighbours), as well as the variability of knee movements, the latter just after heel contact. At each measurement session, patients reported how often they had fallen in the preceding period.Findings: Patients had lower maximum walking speed than controls, and walked with reduced variability, post-operatively even more so. Variability was positively related to number of falls. Pre-operatively, patients had higher λS at the unaffected side, which post-operatively normalized.Interpretation: Slow walking may serve being more cautions. Reducing variability of sagittal knee kinematics appears to reduce fall risk, perhaps involving paying more attention and/or using cocontraction. The pre-operatively higher unaffected side λS could result from attempts to reduce the kinematic demands on the affected leg, “letting go” the unaffected leg. One year after the operation, this problem with unaffected λS had disappeared, suggesting recovery. Further study should include short-term and long-term stability, as well as a quantitative measure of perceived instability.

Biomechanical comparison of hallux valgus correction using the proximal chevron osteotomy fixed with a medial locking plate and the Ludloff osteotomy fixed with two screws - Corrected Proof

Aaron T. Scott, James K. DeOrio, Harvey E. Montijo, Richard R. Glisson — 2010-01-11

Abstract: Background: For moderate-to-severe hallux valgus deformities with a 1–2 intermetatarsal angle in excess of 15°, a proximal first metatarsal osteotomy is indicated. The ideal osteotomy has yet to be defined, but should inherently limit the incidence of dorsal malunion and allow for early ambulation. The present study evaluates the mechanical integrity of two popular first metatarsal osteotomies.Methods: Ten matched pairs of fresh-frozen cadaveric first metatarsals were harvested. In one metatarsal from each pair, a Ludloff osteotomy was created and fixed with two cannulated 3.5mm screws. In the contralateral first metatarsal, a proximal chevron osteotomy was performed and subsequently fixed with a medially applied locking plate. All specimens were mounted within an Instron 1321 servohydraulic materials testing machine and subjected to a plantar-to-dorsal cantilever bending protocol for 1000 cycles.Findings: Two of ten Ludloff osteotomies failed prior to completion of 1000 loading cycles by fracture at the distal screw site, whereas six of ten proximal chevrons failed prior to the 1000th cycle. The mode of failure in this group was by cut-out of the plantar-proximal screw. The bending stiffness of the Ludloff osteotomy exceeded that of the proximal chevron at all measurement points between the 1st and 200th load cycles (P<0.05). After 200 cycles, an inadequate number of plate constructs survived to allow statistical comparison.Interpretation: The results of the present study indicate that the proximal chevron osteotomy fixed with a medially based locking plate exhibits mechanical properties inferior to those of the Ludloff osteotomy under the tested conditions.

The sclerotic line: Why it appears under knee replacements (a study based on the Oxford Knee) - Corrected Proof

Hans A. Gray, Amy B. Zavatsky, Harinderjit S. Gill — 2010-01-08

Abstract: Background: Radiolucent lines and sclerotic margins are often seen on knee radiographs taken a year or longer after knee replacement surgery. Histology has shown that the radiolucent zone is predominantly fibrocartilage and the sclerotic margin is lamellar bone. The reasons for their existence are not clearly understood.Methods: A three-dimensional finite element model of the medial half of the proximal 75mm of a tibia implanted with a knee replacement was created and run over 365 iterations simulating 1year of in vivo post implant remodelling. After each iteration, new material properties were calculated for all elements of the model using established bone remodelling and tissue differentiation rules. For comparison with patient anteroposterior radiographs, “synthetic anteroposterior radiographs” were generated by reverse calculating radiographic densities from material properties of the model after 365 iterations. Von Mises stress of elements in the bone where the sclerotic line is usually seen were calculated after 365 iterations. These values were compared with the same entities assuming no remodelling.Findings: The mean von Mises stress in the sclerotic region was higher when remodelling was assumed than when not, suggesting that the presence of the soft tissue (radiolucent line) increased the stress in the underlying bone.Interpretation: The sclerotic line is caused by the stiffening of bone due to the relatively larger loads seen by the bone just beneath the soft tissue (radiolucent line) adjoining knee replacements.

Effect of wrist position on thumb flexor and adductor torques in paralysed hands of people with tetraplegia - Corrected Proof

Lisa Harvey, Robert D Herbert, Manuela Stadler — 2009-12-25

Abstract: Background: People with tetraplegia often have extensive paralysis of the hand yet retain crude hand function. Their hand function is dependent on manipulating wrist position with the neurally-intact wrist extensor muscles to change the passive tension in paralysed thumb muscles. This moves the thumb in relation to the paralysed index finger enabling basic grasp. The aim of this study was to quantify the effect of wrist position on thumb flexor and adductor torques generated in paralysed hands of people with tetraplegia.Methods: Thumb flexor and adductor torques were measured as the wrist was passively moved from a fully flexed to a fully extended position in 10 people with tetraplegia who had paralysis of all thumb muscles. The relationships between thumb torques and wrist angles were quantified with torque–angle curves.Findings: There was a consistent curvilinear relationship between wrist angle and both thumb flexor and thumb adductor torques. Thumb flexor torques were greatest and thumb adductor torques were smallest when the wrist was fully extended.Interpretation: Wrist position influences the thumb flexor and adductor torques generated in the paralysed hand. This is probably due to the effect of wrist position on the passive tension of the thumb muscles spanning the wrist. These findings have implications for people with C6 and C7 tetraplegia who rely on the passive torques generated by the paralysed thumb muscles for hand function.

Multi-segmental torso coordination during the transition from sitting to standing - Corrected Proof

Molly B. Johnson, Timothy W. Cacciatore, Joseph Hamill, Richard E.A. Van Emmerik — 2009-12-21

Abstract: Background: Research into the multi-segmental mobility of the torso could add to our understanding of the contributions of the head and torso to human movement. The purpose of this study was to determine the motion and temporal coordination of the head and multiple torso segments during the sit-to-stand task.Methods: Thirty-two young, healthy participants performed five trials of the sit-to-stand movement and 6s of sitting. Range of motion and patterns of peak flexion and extension of six segments and joints and cross correlation of pairs of the six torso segments were analyzed from 3-D kinematic data.Findings: Sagittal range of motion for torso joints during the sit-to-stand task was greater than during sitting trials; motion at the lumbar/pelvis joint was greater than at other torso joints. Peak flexion of torso joints occurred earlier than peak extension. Cross correlations at zero lag and time lags of maximum cross correlations varied such that there was greater temporal coordination of intermediate torso segments compared to pairs including the head and pelvis. There was greater temporal coordination of adjacent segment pairs than for pairs that were less proximal to each other.Interpretation: A high degree of mobility occurs within the torso during the sit-to-stand task. Varying coordination patterns suggest that there are regional differences in movement timing within the torso that may relate to segmental differences in functional roles. Employing multi-segmental torso models may indicate different movement strategies within a healthy population and could highlight differences between clinical populations.

Roll-over shapes of the ankle–foot and knee–ankle–foot systems of able-bodied children - Corrected Proof

Andrew H. Hansen, Margrit R. Meier — 2009-12-16

Abstract: Background: The roll-over shape is the effective rocker shape that a lower limb system conforms to during a step. The roll-over shape concept has been explored in detail in adults and has been successfully used in the design, evaluation, and alignment of lower limb prostheses and orthoses. No such analysis exists for the pediatric population. Therefore, the purpose of this study was to investigate the ankle–foot and knee–ankle–foot roll-over shapes in able-bodied children, values that could serve as tools for design and evaluation of lower limb pediatric prostheses and orthoses.Methods: This study describes a multi-center retrospective review of existing motion analysis data (n=153 from three centers). Roll-over shapes were calculated by transforming center of pressure data from a laboratory-based coordinate system into two body-based coordinate systems. Roll-over shapes were then characterized using a circular arc model. Best-fit radii of roll-over shapes for children in three age groups (3–7years, 8–11years, and 12–17years) were compared using the Kruskal–Wallis test.Findings: No significant changes were found in roll-over shape radii between the three age groups (P=0.54 for ankle–foot roll-over shape radii; P=0.12 for knee–ankle–foot roll-over shape radii). The weighted mean of median radii for ankle–foot and knee–ankle–foot roll-over shapes from the three centers were approximately 22% and 17% of body stature, values similar to those seen in adults.Interpretation: Children produce nearly circular knee–ankle–foot roll-over shapes at a young age that are similar to those seen in adults when scaled by body stature.

Effects of foot orthoses on gait patterns of flat feet patients - Corrected Proof

Yu-Chi Chen, Shu-Zon Lou, Chen-Yu Huang, Fong-Chin Su — 2009-12-16

Abstract: Background: Although foot orthotics are widely prescribed for the treatment of flatfoot, the biomechanical effects of such devices are not yet fully clear. Accordingly, this study conducted an experimental investigation to evaluate the effects of orthoses on the gait patterns of patients with flatfoot during level walking.Methods: Eleven adults with flatfoot deformities were recruited. For each participant, kinematic and kinetic data were measured under three test conditions, i.e. walking barefoot, walking with shoes, and walking with shoes and insoles. During each test, the participants’ gaits patterns were recorded and analyzed using a motion analysis system, two Kistler force plates and EVaRT software.Findings: The results showed that walking with shoes and insoles and walking with shoes conditions increased the peak ankle dorsiflexion angle and moment, and also reduced the peak ankle plantarflexion angle and moment. Furthermore, walking with shoes and insoles and walking with shoes conditions increased the peak knee varus moment. The effects of the orthoese on knee and hip were minimal and no significant differences were observed between walking with shoes and insoles and walking with shoes.Interpretation: The results suggested that the foot insoles and shoes developed in this study might benefit the ankle joint in patients with flat feet. In view of the minimal changes between walking with shoes and insoles and walking with shoes, further studies may be required to clarify the interaction between the foot and the insole/shoe.

Wavelet analysis based on time–frequency information discriminate chronic ankle instability - Corrected Proof

A. Martínez-Ramírez, P. Lecumberri, M. Gómez, M. Izquierdo — 2009-12-14

Abstract: Background: Ankle sprains are one of the most common lower extremity injuries. Real time human motion tracking is an accurate, inexpensive and portable system to obtain kinematic and kinetic measurements. The purpose of this study was to discriminate between subjects with chronic ankle instability and subjects with stable ankles through inertial tracking technology and force plates.Methods: Twelve subjects (mean (SD) 23.16 (5.32) years, 174.83 (8.78) cm, 73.58 (17.10) kg) with stable ankles and 13 (mean (SD) 24.69 (5.91) years, 173.31 (9.07) cm, 69.61 (15.32) kg) with chronic ankle instability performed the Star Excursion Balance Test. Time–frequency information based on wavelet decomposition was used for analysing all signals.Findings: Dynamic balance impairment associated with chronic ankle instability was observed in the peak amplitude in the wavelet approximation as well as the absolute sum of the coefficients of the wavelet details of the acceleration, orientation and force signals. These results were found despite Star Excursion Balance Test performance during anterior, posteromedial and posterolateral excursions lead to similar specific reach distances in both limbs in either the chronic ankle instability or stable ankle groups.Interpretation: These parameters could be of great interest in detecting dynamic balance impairment in individuals at risk of sprains that might otherwise go undetected by only reach distance assessment.

Alterations in three-dimensional joint kinematics of anterior cruciate ligament-deficient and -reconstructed knees during walking - Corrected Proof

Bo Gao, Naiquan (Nigel) Zheng — 2009-12-14

Abstract: Background: High risk of cartilage degeneration and premature osteoarthritis development has been clinically observed in anterior cruciate ligament (ACL) deficient knees. The risk has not been significantly reduced even after ACL reconstructive surgery. It was hypothesized that three-dimensional knee joint kinematics has been altered after ACL injury, and the biomechanical alteration has not been fully restored to a normal level after reconstructive surgery.Methods: Spatiotemporal parameters and three-dimensional knee joint rotations and translations were measured in ACL-deficient, ACL-reconstructed, and ACL-intact knees during level walking. The variables were compared between the ACL-deficient and ACL-intact knees, as well as between the ACL-reconstructed and ACL-intact knees.Findings: Altered spatiotemporal variables and key event timings in a gait cycle were observed in both ACL-deficient and ACL-reconstructed subjects. Significant reduction of extension was observed in the ACL-deficient knees during midstance and in the ACL-reconstructed knees during swing phase. Greater varus and internal tibial rotation were identified in the ACL-deficient knees. Although being small in magnitude, these secondary kinematic alterations were consistent throughout the whole gait cycle, and such trends were not eliminated in the ACL-reconstructed knees.Interpretation: Significant abnormalities of spatiotemporal performance and three-dimensional joint kinematics during walking were identified in the ACL-deficient knees. The ACL-reconstructed knees exhibited some improvement in joint kinematics, but not being fully restored to a normal level. Identification of biomechanical alterations during daily activities in ACL-deficient and ACL-reconstructed knees could help better understand clinical outcomes and seek improvement in surgical technique and rehabilitation regimen for ACL injury treatment.

Evaluation of formal methods in hip joint center assessment: An in vitro analysis - Corrected Proof

Nicola Lopomo, Lei Sun, Stefano Zaffagnini, Giovanni Giordano, Marc R. Safran — 2009-12-14

Abstract: Background: The hip joint center is a fundamental landmark in the identification of lower limb mechanical axis; errors in its location lead to substantial inaccuracies both in joint reconstruction and in gait analysis. Actually in Computer Aided Surgery functional non-invasive procedures have been tested in identifying this landmark, but an anatomical validation is scarcely discussed.Methods: A navigation system was used to acquire data on eight cadaveric hips. Pivoting functional maneuver and hip joint anatomy were analyzed. Two functional methods – both with and without using the pelvic tracker – were evaluated: specifically a sphere fit method and a transformation techniques. The positions of the estimated centers with respect to the anatomical center of the femoral head, the influence of this deviation on the kinematic assessment and on the identification of femoral mechanical axis were analyzed.Findings: We found that the implemented transformation technique was the most reliable estimation of hip joint center, introducing a – Mean (SD) – difference of 1.6 (2.7) mm from the anatomical center with the pelvic tracker, whereas sphere fit method without it demonstrated the lowest accuracy with 25.2 (18.9) mm of deviation. Otherwise both the methods reported similar accuracy (<3mm of deviation).Interpretation: The functional estimations resulted in the best case to be in an average of less than 2mm from the anatomical center, which corresponds to angular deviations of the femoral mechanical axis smaller than 1.7 (1.3)° and negligible errors in kinematic assessment of angular displacements.

Teres major muscle activation relates to clinical outcome in tendon transfer surgery - Corrected Proof

2009-12-10

Abstract: Background: In massive rotator cuff tears a teres major (TMj) tendon transfer to the insertion of the supraspinatus (SSp) reverses its adduction moment arm into abduction which is supposed to be an adequate salvage procedure. Analysis of muscle function to find biomechanical ground of such success is scarce.Methods: We compared pre- and postoperative clinical outcome of TMj transfer, i.e. Range of Motion, pain, Constant Shoulder scores and arm force. TMj activation was evaluated in 14 patients suffering massive cuff tears using activation ratios to describe the desired ‘in-phase’ and undesired ‘out-of-phase’ contribution to the external arm moment. Additionally, we analyzed activation of the latissimus dorsi (LD) and the medial part of the deltoids (DE). The activation ratios were compared to controls and TMj activation ratios were related to clinical outcome.Findings: TMj tendon transfer improved arm function. Pre-operatively, we observed ‘out-of-phase’ abduction activation of TMj and LD. After transfer patients activated TMj according to its new anatomical position. ‘Out-of-phase’ LD abduction activation persisted. The clinical improvements coincided with changes in activation ratio of TMj.Interpretation: ‘Out-of-phase’ TMj adductor activation is associated with compromised arm function in patients with irreparable cuff tears. After transfer, TMj is activated in correspondence with its new anatomical function, which was supportive for the improved arm function.

Gait parameters and stride-to-stride variability during familiarization to walking on a split-belt treadmill - Corrected Proof

Joseph A. Zeni, Jill S. Higginson — 2009-12-10

Abstract: Background: Subjects unfamiliar to walking on a split-belt treadmill may initially demonstrate an altered gait pattern or increased variability of gait parameters. While previous investigations have examined kinematic variables associated with familiarization time, the objective of this study was to determine the familiarization period required to obtain the most reproducible gait pattern through the assessment of kinetic, kinematic and spatio-temporal parameters during a single session of treadmill walking.Methods: Eleven healthy subjects participated in a single bout of treadmill walking which lasted 9min. Kinematic and kinetic data were collected from the first 30s of each minute, beginning when the treadmill reached full speed. Means and standard deviations for knee flexion at heel strike, ground reaction forces, step width and step length were obtained to examine the changes in each variable over the 9min. Mean r2 values were evaluated for changes in variability from one stride to the subsequent stride for sagittal plane hip, knee and ankle joint angles and moments, as well as for vertical and horizontal ground reaction forces.Findings: Significant reductions in variability were found for vertical and horizontal ground reaction forces, knee flexion at heel strike and step length over 9min. Only step width showed a change in the mean value across trials. There were no increases in r2 values after the 5th min for any of the gait variables.Interpretation: The results suggest that in order to collect accurate data for gait analysis, subjects should be familiarized to the split-belt treadmill for at least 5min prior to data collection.

Cruciate ligament tensile forces during the forward and side lunge - Corrected Proof

2009-12-10

Abstract: Background: Although weight bearing lunge exercises are frequently employed during anterior cruciate ligament and posterior cruciate ligament rehabilitation, cruciate ligament tensile forces are currently unknown while performing forward and side lunge exercises with and without a stride.Methods: Eighteen subjects used their 12 repetition maximum weight while performing a forward lunge and side lunge with and without a stride. A motion analysis system and biomechanical model were used to estimate cruciate ligament forces during lunging as a function of 0–90° knee angles.Findings: Comparing the forward lunge to the side lunge across stride variations, mean posterior cruciate ligament forces ranged between 205 and 765N and were significantly greater (P<0.0025) in the forward lunge long at 40°, 50°, 60°, 70°, and 80° knee angles of the descent phase and at 80°, 70°, 60° knee angles of the ascent phase. There were no significant differences (P<0.0025) in mean posterior cruciate ligament forces between with and without stride differences across lunging variations. There were no anterior cruciate ligament forces quantified while performing forward and side lunge exercises.Interpretation: Clinicians should be cautious in prescribing forward and side lunge exercises during early phases of posterior cruciate ligament rehabilitation due to relatively high posterior cruciate ligament forces that are generated, especially during the forward lunge at knee angles between 40° and 90° knee angles. Both the forward and side lunges appear appropriate during all phases of anterior cruciate ligament rehabilitation. Understanding how forward and side lunging affect cruciate ligament loading over varying knee angles may help clinicians better prescribe lunging exercises in a safe manner during anterior cruciate ligament and posterior cruciate ligament rehabilitation.